It was shown by J. Willard Gibbs during the nineteenth century that it would not be possible to nucleate new growth on a perfectly flat surface of a solid by simple addition of atoms from a melt except under very high supercooling or supersaturation. Later, it was concluded by others that a perfect crystal can not grow at low supersaturation on singular surface such as the &lt;100 &gt; surface of the gallium aluminum arsenide system. However, it is known that crystals of high macroscopic crystallographic perfecton actually do grow at low supersaturation on the &lt;100 &gt; surface (as well as on other singular surfaces) of the gallium aluminum arsenide multicomponent system. In fact, the conventional method of growing a GaAs-GaAlAs double heterostructure junction laser makes use of a &lt;100 &gt; oriented substrate to provide the growth axis for liquid phase epitaxy.
GaAs--GaAlAs double heterostructure laser thus grown by this conventional method contains a concentration of intrinsic nonradiative recombination centers which is greatly in excess of the thermodynamic equilibrium concentration under growth conditions. These defects cause the devices to degrade and fail in operation or when optically pumped. The devices grown in this way are observed to fail by growth of a "dark line defect" if the device contains a threading dislocation, or by growth of "dark spot defects" if the devices contains inclusions of aluminum oxide, graphite or other foreign matter. If neither of the above gross defects is present, the conventional devices degrade by becoming more or less uniformly dimmer.
Analysis of both short-time modes of failure shows that a concentration of nonradiative recombination centers of about 10.sup.19 /cm.sup.3 must exist in the active layer and/or in the p-type alloy layer in the as-grown device. Analysis of the thermodynamic properties of the materials under growth conditions shows that these nonradiative recombination centers are a complex of two arsenic vacancies and one aluminum antisite defect and that the actual concentration is about 100 times the equilibrium concentraton under growth conditions. Thus, although the crystalline layers are macroscopically perfect (i.e. smooth and free of defects visible under an optical microscope) they have a high density of defects on the atomic scale.
It was realized heretofore that there was a concentration of the particular nonradiative recombination center V.sub.As.sup.+1 Al.sub.As.sup.-2 V.sub.As.sup.+1 present in amounts more than 100 times the number that would be expected from equilibrium considerations.
The formation of darkline, DL, and darkspot, DS, defects are significant degradation short-time modes for GaAlAs double heterostructure lasers as summarized in the following literature articles:
a. P. Petroff and R. L. Hartman, Appl. Phys. Lett. 23, 469 (1973) PA1 b. R. Ito, H. Nakashim, S. Kishino and O. Nakada, IEEE J. Quant. Elect. QE-11, 551 (1975) PA1 c. P. W. Hutchinson, P. W. Hutchinson, P. S. Dobson, S. O'Hara and D. H. Newman, Appl. Phys. Lett. 26, 250 (1975) PA1 d. J. A. Van Vechten, J. Electrochem, Soc. 122, 1556 (1975)
A review article of background interest for practice of this invention is "Heterostructure Junction Lasers" by M. B. Panish and I. Hayashi published on pages 235-328 in the book "APPLIED SOLID STATE SCIENCE, Vol. 4, Advances in Materials and Device Research", Academic Press, 1974.
The practice of this invention will be distinguished hereinafter from the disclosures of the following identified U.S. patents for which summary is presented:
I. U.S. Pat. No. 3,556,875, filed Jan. 3, 1967 by H. Holloway et al and issued January 1971 for "Process for Epitaxially Growing Gallium Arsenide on Germanium" discloses a method for the epitaxial growth from the vapor phase of device quality gallium arsenide on a monocrystalline germanium substrate having an exposed surface oriented between the (100) and the (111) crystal planes preferably at or between the (311) and (511) planes. It is stated therein that prior art methods have attempted to grow gallium arsenide on the (100), (111) and (110) crystal planes of a germanium substrate, and that crystals grown upon these planes have not been of device quality. That is, they are macroscopically imperfect.
II. U.S. Pat. No. 3,636,412, filed Dec. 23, 1968 by Y. Takeishi et al and issued Jan. 18, 1972 for "Oxide Coated Semiconductor Device Having [311] Planar Face" discloses a semiconductor device (for example, a planar transistor MOS-diode, or MOS-type field effect transistor) having a semiconductor substrate formed of a single crystal wherein the flat top surface of the substrate consists of a [ 311] crystal plane or one inclining to an extent of .+-.5.degree. with respect to said [ 311] crystal plane. The orientation is chosen to maximize the speed of growth and/or etching.
The semiconductor substrate may consist of a single crystal semiconductor formed of a single element such as silicon or germanium, or compounds of Groups III and V. The semiconductor device is fabricated by forming layers on the lattice plane by means of a vapor phase or epitaxial growth method, diffusion method or alloying method and also by subjecting the substrate to various types of processing, for example, photographic etching, or chemical etching.
III. U.S. Pat. No. 3,721,583 filed Dec. 8, 1970 by A. E. Blakeslee and issued Mar. 20, 1973 for "Vapor Phase Epitaxial Deposition Process for Forming Superlattice Structure" discloses a vapor phase epitaxial process for forming a superlattice structure comprising alternate layers of different semiconductor materials on a substrate, in which superior macroscopic perfecton is obtained upon a (311) substrate. It is stated that Ga.sub.x Al.sub.1-x As is one of the semiconductor systems which can be grown as epitaxial films and fashioned into superlattices in accordance with the invention.
It is stated that upon examining the product formed in accordance with an example of a wafer with a (100) orientation which had a curved edge, with an electron microscope, some deviations from a completely planar surface were observed. It was noted upon close examination that the epitaxial layers deposited around this curved edged contained a section with a much flatter superlattice structure than the remainder of the wafer. The orientation of this curved section was found to be very close to the (311) plane.
It is stated that, a wafer exactly as used in the noted example except with (311) orientation was substituted for the wafer and the process run repeated. The superlattice structure and the resultant layers are said to have turned out to be much flatter than those obtained in utilizing a (100) substrate, and that it was found to be possible to produce successive layers of extreme planarity.